Our research program focuses on several cell cycle proteins that are targets for the rational design of anti-cancer drugs. Two are homologous human proteins (CksHs1 and CksHs2) that are critical components of the cell cycle. These mutants were chosen to characterize the components of the metal binding sites and residues important for the multimeric structure. We have crystals of the entire ribonucleotide reductase enzyme complex. The intense beam at SSRL will provide us with the quality of diffraction that will be needed to collect data at the plate distance necessary.